Yep, lots of good advice above. Repositionings are usually the best value, especially if you like the idea of an ocean voyage rather than a cruise around a pond - plenty of sea-days in which to immerse yourself in the ship, the one-off activities and a good book on deck. If you are based in Toronto or more generally North America, then yes the VacationsToGo website is an excellent starting point:
http://www.cruisehotsheet.com/region...itioning-0.htm
and I agree, CruiseComptete.com can usually trim off a little on those fares.
If you are wanting solo-occupancy however, these fares don't apply. I find repositionings on MSC Cruises booked through a UK agent will usually be hard to beat - £25/£35/£45 per night solo occupancy of inside/outside/balcony (that is US$560 for a 14-night Transatlantic). This is cruise only, including taxes, before discounts.
With a repo, choose your start and end points carefully to get best value from your miles or to be covered by a low-cost airline. Also, timings. To avoid an unwanted and expensive hotel stay before or after the cruise, make sure you allow plenty of leeway in your flight times and ideally choose a carrier with more than one daily flight.